Two identical capacitors have same capacitance C. One of them is charged to the potential V and other to the potential 2V. The negative ends of both are connected together. When the positive ends are also joined together, the decrease in energy of the combined system is :
- 14CV2
- 34CV2
- 12CV2
- 2CV2
Answer
(1) 14CV2
Solution
When like plates are joined, charge is conserved and both capacitors reach a common potential:
qnet = CV + C(2V) = 3CV, VC = qnet2C = 3V2
Energy before = 12CV2 + 12C(2V)2 = 52CV2
Energy after = 12(2C) ( 3V2 )2 = 94CV2
decrease in energy = 52CV2 - 94CV2 = 14CV2 (lost as heat during charge flow)
Answer: (1)